I am new to Zwift and a relatively novice rider. Just looking at the 10-12wk FTP builder, I see there are generally x4 workouts a week, but what days do I train on? Surely I don’t do x4 days on the trot and then take x3 rest days or is it day on, then day off? Any assistance would be much appreciated.
Andy

The workout is structured as you can see in the weekly plan. I mean, for instance: you ride on monday & tuesday; then you rest on wednesday and work again on thursday & friday. Then rest sat & sunday. Other weeks the organization of the work can change.
Have a look to the FTP Builder plan and you 'll see how the workout is structured every week with differents days.

What about the remaining 2 days.
Why not put the resting days in the calendar, instead of letting the rider figure out what days he should ride.
Or just let the rider decide which 3 days he will rest. There is no reason to have a rest day included in the schedule.

For the plans with a 5 day week, I always operated under the premise that the days were 1-5 / Monday - Friday and that it’s assumed that weekend rides would be done IRL away from the trainer and were ‘rider’s choice’ or add’l rest day(s) as needed.

That generally alligned well with my schedule and made it easy to remember which day (#) it was.